The goal of the proposed research is to advance our understanding of the molecular mechanisms that govern selective gene transcription. The specific objective of this study is to isolate a particular DNA sequence in the form of chromatin from two different cell types of the same organism. In one of these cell types the sequence of interest is actively transcribed while in the other it is not. A detailed comparison of the structure and protein composition of the isolated chromatin in its transcriptionally-active and dormant states will be made. The sequence chosen for study is the 5S DNA of Xenopus. In the frog, Xenopus laevis, the sequences coding for 5S ribosomal RNA form a developmentally regulated multigene family. 5S genes are present in many thousand copies per genome and different types of 5S genes are expressed in oocytes and somatic cells. The oocyte-type 5S DNAs have been isolated, cloned and now sequenced. The location of restriction enzyme cleavage sites in the sequence of oocyte-type 5S DNA and the abundance of 5S DNA in the Xenopus genome make this gene well suited for isolation as chromatin. It has been demonstrated recently that 5S RNA can be synthesized in vitro from isolated oocyte chromatin by the addition of homologous RNA polymerase III. Similarly, 5S RNA can be synthesized in vivo after the injection of purified 5S DNA into Xenopus oocytes or in vitro with oocyte extracts. Faithful transcription of protein-free DNA with purified polymerase III alone has not been observed. Thus it appears that the accurate and selective transcription of 5S RNA requires some additional factor(s). The present study will attempt to elucidate the structural and compositional differences between actively transcribed 5S gene chromatin and transcriptionally-inactive 5S gene chromatin. Further, an attempt will be made to determine which chromatin components promote (or suppress) transcription of this gene.